Variable delay line



Nov. 26,

FIG. I..

Variable Bias Source Maqncloslriclivo I Malerial 20 Amplifier Switch Amplifier Write 3 Read -Out Terminal Terminal Ff II 47 Me -49 -50 is ,4. 4 7% Lil -52 53 54 .7 Variable Bras Source wrilo- Terminal INVENTOR AGENT United States Patent VARIABLE DELAY LINE Theodore H. Bonn, Philadelphia, Pa., assignor to Sperry Rand Corporation, a corporation of Delaware The present invention relates to variable acoustic delay lines and is more particularly concerned with such structure's utilizing magnetostrictive material.

Acoustic delay lines are presently utilized in many electronic applications and may be employed for instance in memories for use in computing apparatuses. Reference is made to U. S. Patent No. 2,629,827, I. P. Eckert, Jr., et al., issued February 24, 1953, for: Memory System, which patent discusses delay line structures for use in a computer memory. In general, such a memory operates in conjunction with recirculation means such as an amplifier, whereby information to be stored as a pulse sequence may be fed to one end of the delay line, may be caused to propogate as an acoustic signal down the said delay line, and may then be caused to recirculate to the input of the line.

Inasmuch as the acoustic propogation down such a line takes a finite time, the successive recirculation of information through an acoustic delay line, of the type contem plated, efiectively stores the information being recirculated. The foregoing Eckert patent discloses various forms of delay lines capable of functioning in the above described manner; and at Figures 23 throught thereof discloses acoustic lines employing magn-etostrictive materials. The present invention relates to an improvement of this form of acoustic delay line and is especially concerned with the provision of a magnetostrictive delay line wherein the delay imposed may be readily varied, thereby to permit utilization of such a line in various applications requiring such a variable delay feature.

In accordance with the present invention, such an improved delay line is effected by providing a transmission medium for acoustic waves, comprising a magnetostrictive material. This transmission medium cooperates with plural magnetic transducers whereby information may be fed into and read out of the transmission medium; and the said transmission medium further includes bias means associated with the medium itself, for varying the propagation time of acoustic waves in the medium.

It is accordingly an object of the present invention to provide an improved delay line structure.

A further object of the invention resides in the provision of a delay line, the delay time of which may be readily varied.

Still another object of the present invention resides in the provision of a recirculating memory employing a variable delay line of magnetostrictive material.

Still another object of the present invention resides in the provision of a delay line which may be readily compensated for temperature variations, whereby the propagation time of the said line may be made constant despite variations in ambient conditions.

Another object of the present invention resides in the provision of a variable delay line capable of utilization in pulse time modulation and in frequency modulation systems.

A further object of the present invention is the provision of a memory system which may be smaller, more 2 rugged in configuration, and less subject to operating failures than other forms of memories utilized heretofore.

The foregoing objects, advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings.

Figure 1 illustrates one form of delay line constructed in accordance with the present invention and utilizing a pair or" magnetic transducers; and

Figure 2 illustrates a further embodiment of the present invention utilizing a variable delay line cooperating with three or more transducers for the selective reading and writing of information intermediate the ends of the line.

Referring now to Figure 1, it will be seen that an acoustic delay line constructed in accordance with the present invention, may comprise a magnetostrictive element 16, formed, for example, of well known iron and nickel alloys exhibiting magnetostriction effects. Reference is made to the text of Bozorth Ferromagnetism, D. Van Nostrand & Co. (1951), page 627 et seq.; and page 684 et seq., which discusses materials capable of utilization in the present invention, and the properties of such materials. In general, these magnetostriction effects are such that the application of a magnetic field, such as may be produced for instance by a magnetic transducer, imposes a physical strain upon the magnetostrictive material, and this strain may in turn be propagated down a length of such material in the form of an acoustic wave.

The element 10 may comprise an elongated bar, tube, tape, or wire entirely of magnetostrictive material, or may further comprise relatively small sections of such magnetostrictive material, physically coupled to one another by further acoustic transmission mediums such as ceramic, glass or metal. In providing a delay line, in accordance with "the present invention, a first magnetic transducer 11, carrying an input signal coil 12 and a bias coil 13 thereon, may be dis-posed adjacent one end of the magnetostrictive element 10; and a further transducer 14, also carrying a bias winding 15 and :a signal winding 16, may be disposed adjacent the other end of the said element 10.

In operation, signals may be coupled to the winding 12 of transducer 11 at terminals 17 and such signals impose an acoustic wave on the medium 10 which wave is propagated down the length of the said medium to induce a further potential in the transducer 14, and more particularly in the winding 16 thereof, which may appear at the output terminals 13. When operated as a dynamic memory, a recirculation amplifier may be coupled between the terminals 17 and 18, whereby signals induced in the winding 16 are selectively recirculated to the winding 12, thereby to impose a further acoustic wave on the medium 10. The bias windings 13 and 15 are employed on the heads 11 and 14 respectively, to assure that a fundamental frequency rather than a second harmonic thereof is propagated down the magnetostrictive medium 10, such a bias consideration being required inasmuch :as magnetostriction effects ordinarily vary in accordance with the second power of the applied transducer field. The medium 10 is provided with angularly disposed faces 19 and 20 at the ends thereof, as shown, to prevent reflections of waves propagated toward those ends. Other forms of termination may, of course, be utilized in this respect.

The foregoing form of acoustic delay line is essentially shown in the previously identified patent to J. P. Eckert, in, et al. The simple line thus far described, however, includes the operational limitation that the time of propagation of acoustic waves through the said line is aifected, for instance, by conditions of ambient temperature, and

therefore this propagation time varies in response to a a variations in such ambient conditions. The line in its simplest form must ordinarily be used, therefore, in conjunction with rather complex apparatus serving to control ambient conditions, thereby making an over-all system rather expensive and highly subject to operating failures.

It has been found that these prior requirements, for instance of temperature control, may be obviated, however, by the provision of a variable bias source coupled to the rnagneto-strictive medium itself; and it its broader aspects the present invention thus provides an acoustic delay line the delay time of which may be readily maintained constant by appropriate variations in such bias in opposition to changes in ambient condition. In addition, the arrangement of the present invention provides a delay line, broadly, the delay time of which may be readily varied when variable delay requirements are desirable. Thus, the transmission medium 14) of Figure l carries an elongated coil 21' uniformly disposed on the said medium between the transducers 11 and 14, the said coil being coupled to a variable bias source 2.2. The said bias source 22 may be a D. C. source "and may also comprise a varying signal which is generally of a low frequency in comparison with the repetition rate of pulses being propagated down the line. In addition, the source 22 may be selectively variable whereby the delay exhibited by the line can be varied for purposes such as pulse time modulation; or the said bias source 22 may be varied in response to variations in detected time of propagation of pulses through the line (e. g. by a servomechanism) or in response to temperature variations as detected by a thermostatic element, thereby to maintain the propagation time of the line constant despite variations in ambient conditions.

Thus, the provision of a variable bias source 22, in combination with an elongated coil 21 carried by the acoustic medium lli, serves as a convenient means for controlling the velocity of acoustic propagation in the magnetostrictive delay line, and therefore controls the time delay exhibited by that line. This effect follows inasmuch as the velocity of acoustic propagation in a magnetostrictive material is represented by the equation:

where E is Youngs modulus for the particular magnetostrictive material employed; and p is the density of the magnetostrictive material. By changing the bias imposed upon the magnetostrictive material, both Youngs modulus and p are changed, but the change in Youngs modulus, E, greatly predominates, so that a variation in bias does in fact effect a variation in the velocity of acoustic propagation through the magnetostrictive material. When the system is utilized as a dynamic memory, therefore, a constant delay time may be readily achieved. The system also can be employed, of course, in other applications where a readily controllable delay time is required, such as in selective gating applications or in pulse time modulation systems, and in this latter respect still further variations may be employed. Thus, referring to Figure l, the head 11 and/ or the head 14 may be movably mounted with respect to medium whereby a physical change in distance between the heads 11 and 14 may be effected to perform the function of or to supplement the variable bias provisions.

The arrangement of Figure 2 illustrates a modification of the foregoing structure, and is especially concerned with a magnetostrictive delay line system wherein three or more heads are employed in conjunction with the transmission medium. Thus, this modification may comprise an acoustic transmission element 30, again formed of a magnetostrictive material. A plurality of magnetic transducers 31 through 35 are again disposed adjacent the said material 30 with the appropriate. coils of the terminating transducers 31 and 35 being connected to 4 one another via a recirculation amplifier 36. As was discussed previously, signals coupled from the output of amplifier 36 to the transducer 31 are propagated down the material 30 as an acoustic wave and induce a further signal in the transducer 35 which is again applied to the amplifier 36, thereby to provide a recirculating storage condition. The recirculation amplifier 36 is further provided with a write terminal 37 and a read-out terminal 38 whereby information may be selectively introduced or read out of the recirculation path. Inasmuch as a recirculation amplifier such as 36 need be used only between the bcginnin'g and end of the delay line, however, a considerable economy in structure is effected, and more versatile operation is achieved, by providing intermediate transducers such as 32, 33 and 34 for the selective writing in and reading out of information intermediate the ends of the line. Such a structure may in fact utilize an electronic switch 40 coupled to the appropriate windings on the transducers 32, 33 and 34, and also coupled to a write terminal 41 via an input amplifier 42 and to a read-out terminal 43 via an output amplifier 44. The intermediate heads 32, 33 and 34 may thus be utilized for rapid access to the delay line and do not require separate recirculation amplifiers for proper operation of the system.

Variation in the delay time of the line is again effected by the provision of a bias coil 45 coupled to a variable bias source as of the type described previously. In accordance with this modified form of the present invention, the coil 45 comprises a plurality of individual winding sections 47 through 50 inclusive, and these may, if desired, be connected in series, in parallel, or in series parallel with one another. The sections whether individual or interconnected are respectively disposed intermediate adjacent transducers on the line, and the current in individual sections may be controlled by variable shunt resistors 51 through 54, inclusive. By this arrangement of wind ing portions, therefore, the propagation time between individual heads may assume the same percentage of the total propagation time as the spacing of the heads is of the total spacing. Thus, a constant average velocity can be assured between the individual transducers employed, whereby the system may be employed in dynamic memories wherein it is required that the total delay, as well as predetermined submultiples thereof, remain constant.

The system may also be employed in pulse time modulation apparatuses, and when so employed it should be noted that the bias source 46 may in fact be caused to vary considerably in accordance with an input signal during the transit of a single pulse through the line. Inasmuch as the magnetostrictive medium 30 responds to the average bias imposed on the said medium, however, the time of propagation will vary as the average of the bias signal, whereby the delay device, with the varying bias signal shown, acts to integrate the changes in velocity caused by the said bias sign-a1. These characteristics of varying delay time and of signal integration may, therefore, be employed in many forms of apparatus requiring such operational characteristics; and it must therefore be understood that the foregoing methods of utilization of the device are meant to be illustrative only and are not limitative of the present invention.

When utilized in a dynamic memory, a plurality of magnetostrictive elements of the type discussed previously can be employed; and when such elements cooperate with pluralities of heads, in the manner described in reference to Figure 2, the resulting memory, although relatively inexpensive, nevertheless has a large storage capacity and rapid access. In addition to the dynamic memory and pulse time modulation uses of the present invention, the. system may also be employed for changing the'time scale of a digital computer as well as in synchronizing plural pulse systems which operate at sub stantially the. same frequency, provided the average difference in frequency of the said plural pulse systems is zero over times comparable to the individual time of the line utilized.

While I have described preferred embodiments of the present invention, many variations will suggest themselves to those skilled in the art, and all such variations as are in accord with the principles discussed previously, are meant to fall within the scope of the present invention.

Having thus described my invention, 1 claim:

1. A variable delay line comprising an elongated transmission medium of magnetostrictive material, first and second magnetic transducers spaced from one another adjacent said transmission medium for initiating and intercepting acoustic pulses in said medium, and means intermediate said transducers for supplying a bias to said magnetostrictive material, thereby to control the velocity of propagation of said acoustic pulses in said medium between said transducers, said last-named means comprising a bias coil adjacent said material between said transducers, and an energization source coupled to said coil for effecting a controllable bias current flow in said coil.

2. A variable delay line comprising an elongated acoustic transmission medium including magnetostrictive material, a first magnetic transducer adjacent said medium for selectively initiating an acoustic wave in said medium, a second magnetic transducer adjacent said medium and spaced from said first transducer, said second transducer being responsive to waves propagated by said medium, a bias winding carried by said magnetostrictive material between said first and second transducers, and a variable bias signal source coupled to said bias winding.

3. The variable delay line of claim 2 including amplifier means between said first and second transducers whereby signals may be recirculated through said transmission medium.

4. A variable delay line comprising an acoustic transmission medium including magnetostrictive material, at least three magnetic transducers spaced from one another adjacent said transmission medium for selectively initiating and intercepting acoustic waves in said medium, and variable bias means coupled to said transmission medium, said bias means being disposed between each of said transducers and the other transducers adjacent thereto, said bias means comprising a plurality of coil portions carried by said transmission medium, and a source of variable potential coupled to said coil portions.

5. A control system comprising an elongated transmission medium including magnetostrictive material, first and second transducers disposed respectively adjacent opposite ends of said medium, a third transducer adjacent said medium between said first and second transducers, a first bias coil between said first and third transducers, a second bias coil between said second and third transducers, means coupling said first and second coils to one another, and a source of bias potential coupled to said first and second coils.

6. The control system of claim 5 in which said first and second coils are connected in series, said source of bias potential comprising a variable potential source coupled across said series connected coils.

7. The control system of claim 5 wherein the ratio of turns on said first and second coils, respectively, equals the spacing ratio between said first, third, and second transducers.

8. The control system of claim 5 including a recirculation amplifier coupling said first and second transducers to one another, and further amplifier means coupled to said third transducer.

9. A signal control system comprising an elongated acoustic transmission medium including magnetostrictive material, a first transducer adjacent said medium for selectively propagating an acoustic wave through said medium, a second transducer adjacent said medium and spaced from said first transducer for intercepting acoustic waves in said medium, and bias means substantially continuously disposed between said first and second transducers adjacent said medium for selectively applying a substantially uniformly distributed bias to said medium between said transducers, said bias means comprising an elongated coil surrounding said medium, and a source of selectively variable potential coupled to said coil.

10. The system of claim 9 wherein each of said transducers comprises a magnetic recording head.

11. A signal control system comprising an acoustic transmission medium including magnetostrictive material, first and second magnetic transducers spaced from one another adjacent said medium, a third magnetic transducer adjacent said medium between said first and second transducers and substantially colinear with said first and second transducers, first magnetic bias means interposed between said first and third transducers, and second magnetic bias means interposed between said second and third transducers.

12. The signal control system of claim 11 wherein each of said first and second bias means is variable.

13. A signal control system comprising an acoustic transmission medium including magnetostrictive material, a plurality of magnetic transducers spaced along said medium and substantially colinear with one another, and variable magnetic bias means adjacent said transmission medium between each of said plurality of transducers for selectively varying the velocity of acoustic propagation through said medium between said transducers.

14. A variable delay line comprising an elongated transmission medium including magnetostrictive material, first transducer means adjacent said medium for initiating an acoustic wave in said medium, second transducer means adjacent said medium and spaced from said first transducer, said second transducer being responsive to waves propagated by said medium, and means adjacent said medium intermediate said first and second transducers for controlling the velocity of propagation of acoustic waves in said medium, said last-named means including means for producing a controllable magnetic flux in said magnetostrictive material between said first and second transducer means.

15. An acoustic delay line comprising a transmission medium including magnetostrictive material, first and second magnetic transducers spaced from one another adjacent said medium, said transducers respectively including means for initiating and intercepting acoustic waves in said magnetostrictive material, at least one of said transducers also including first bias means for controlling the harmonic content of acoustic waves produced in said medium, and second bias means adjacent said medium intermediate said transducers for controlling the velocity of propagation of said acoustic waves in said medium, said second bias means including means for producing a controllable magnetic flux in said magnetostrictive material intermediate said transducers.

OTHER REFERENCES March 1951, pp. Magnetostrictive Delay Line by Electrical Communication, vol. 28, 46-53, article entitled E. M. Bradburd. 

